The present invention relates to a portable trimmer such as a shoulder-type portable trimmer or a hedge trimmer having a cutter, and in particular, to a portable trimmer equipped with a brake device for preventing a cutter from being operated unexpectedly.
A portable trimmer such as a shoulder-type portable trimmer, a backpack-type portable trimmer, a hedge trimmer or the like generally employs a driving mechanism which transmits the power generated by an internal combustion engine to a cutter through a centrifugal clutch. In these portable trimmers, as disclosed, for example, in the Japanese Patent Publication No. Sho 52-12089, a brake device is proposed in which a friction member such as a brake shoe, a brake band or the like slidably engages with a clutch drum of the centrifugal clutch to prevent a cutter from free rotation in order to provide improved safety at a starting time thereof. According to the device disclosed therein, when an operator grips a brake lever, the brake device is actuated to stop rotation of the clutch drum and whereby the cutter is prevented from being rotated unexpectedly. After having released the brake lever and thereby de-activating the brake device, the operator holds a throttle lever, adjusts a throttle opening of a throttle valve to control the power from the internal combustion engine, and thereby drives the cutter through the clutch drum to perform trimming work.
In this type of trimmer, however, if the brake device is released while the throttle lever is being gripped, the cutter might suddenly start to rotate at high speed before the safety at surrounding work operations is confirmed and might possibly cause a serious accident.
The object of the present invention is therefore to solve the problem described above and to provide a portable trimmer with improved safety.
The object of the present invention described above can be achieved by a portable trimmer which comprises: an internal combustion engine; a centrifugal clutch having a clutch drum; a cutter driven by power generated by the internal combustion engine which is transmitted via the centrifugal clutch; a throttle valve; a manual throttle lever for controlling output power of the internal combustion engine by adjusting an opening of the throttle valve via a throttle wire; a friction member arranged opposite to the clutch drum of the centrifugal clutch; a moving member which is connected to the friction member and moves the friction member between a braking position to be pressed against the clutch drum and a non-braking position to be spaced from the clutch drum to release the braking action; a manual release device for moving the moving member from the braking position to the non-braking position; and a release restricting device for controlling activation of the manual release device; the release restricting device having a retaining device whose operation interlocks with a movement of the throttle wire which is controlled by operation of the throttle lever and maintains the release device to be restricted from being released by the release restricting device in a range which is equal to or higher than a predetermined revolution number of the internal combustion engine.
In the present invention, when the centrifugal clutch is under a braking condition, the moving member is in the braking position where the friction member is pressed against the clutch drum. Under this condition, when the operator operates the throttle lever, the release restricting device is activated interlocking with the movement of the throttle wire. When the revolution number of the internal combustion engine is in a range equal to or higher than a predetermined value, the retaining device maintains said release device to be restricted from being released by the release restricting device.
According to the present invention, in the range where the revolution number of the internal combustion engine is equal to or higher than the predetermined value, the operator cannot activate the manual release device, since the actuation of the manual release device is restricted by the release restricting device, whereby the cutter is kept under a braking condition and is prevented from being rotated suddenly. It enables providing improved safety. In addition, since the release restricting device is activated by the movement of the throttle wire, the releasing motion of the manual release device can be controlled in an interlocking manner with the operation of the throttle lever whereby the configuration thereof can be simplified and can be compact.
The present embodiment further comprises a swing member which is connected to an intermediate portion of the throttle wire and is swung by movement of the throttle wire. The release restricting device has a finger member which is pivotably mounted on the same pivoting shaft as the swing member so as to rotate with respect to each other. The retaining device is a spring. The finger member has a claw portion which is pressed against a locking surface formed on the moving member by the spring. The present embodiment further comprises a stopper which is releasably provided between the swing member and the finger member for preventing the finger member from rotating with respect to the swing member more than a predetermined angle by the spring, and wherein the stopper is activated when the revolution number is equal to or more than the predetermined value and is released when the revolution number is under the predetermined value.
In the present embodiment, the stopper is unlocked when the swing member is swung to a high revolution side due to the movement of the throttle wire and the revolution number goes up into a range equal to or higher than the predetermined value, whereby the finger member is pushed by the spring and the claw portion is engaged with the locking surface. When the operator further operates the throttle lever to an accelerating side, the swing member is further pulled by the throttle wire, and the swing member rotates relative to the finger member to allow the throttle wire to be moved further. On the other hand, when the swing member is swung back to a low revolution side due to the movement of the throttle wire and the revolution number goes down below the predetermined value, the stopper is unlocked and the finger member is rotated together with the swing member, whereby the claw portion is disengaged from the locking surface. According to the present embodiment, the release restricting device with a simple configuration acts to make the manual release device inoperable when the revolution number of the internal combustion engine is equal to or higher than the predetermined value, and acts to make it operable to allow the braking of the clutch drum to be manually released when it is less than the predetermined value.